Starch products of stable viscosity



2,929 ,s11 STARCH Pnonucrs or STABLE vrscosrrv Application November 28, 1958 Serial No. 777,549

. Claims. (Cl. also-233.3

(Granted under Title 35, US." Code (1952), see. 266) No Drawing.

A non-exclusive,irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grantsublicens'es for such purposes, is hereby granted to the Government of the United-States of America.

This invention relates to the production 'of starch prodnets of improved stability. More specifically, it relates to novel and useful starch derivatives characterized by their ability to form cooked pastes of high stability and clarity, to have greater resistance to gelling of the pastes upon cooling, and to regain their original hot paste viscosity uponreheating the cold pastes as compared to untreated raw starch.

In Patent No. 2,894,945 dialdehyde starch formed by reaction of starch with periodate was oxidized with chlorous acid under specific conditions for the essentially-complete conversion of the aldehyde groups to carboxyl groups which products after neutralization are named dicarboxyl starches. This class of novel products are starch derivatives in granular form possessing valuable properties of cold water solubility with high viscosity and clarity.

" i itfidg itates Pa ent I ice , performance of the epichlorohydrin etherified dicarboxyl longed periods of time is of the greatest importance in high-speed gluing machine rolls.

dependent upon its viscosity.

Aqueous pastes of the above products are suitable for use 1 to .005 mole equivalentof'the epichlorohydrin, and then.

consecutively oxidized with .periodate, and chlorous acid,

respectively, cross-linked dicarboxyl starches are obtained whose alkali or ammonium salts in aqueous solution show remarkably improved, viscosity stability at high temperaturesover prolonged periods oftime.

Itis known in the art that starch can be reacted with epichlorohydrin, formaldehyde and other cross-linking agents. Such products are not gelatinizable exceptunder immoderate conditions, When slightly cross-linked, pastes of extremely high'viscosity are' obtained. Highly cross-linked starch forms a two-phase system containing precipitated unswollen starch granules which have no appreciable viscosity characteristics. 'It'is also known that polysaccharides can be periodate and chlorous acid to yield dicarboxylated products. Dicarboxyl1starches, prepared in accordance with said Patent No. 2,894,945 are readily gelatinized in hot aqueous dispersions to give pastes of high initial viscosity and clarity.', However, during heating of the pastes at approximately 92" .'C.. the viscosity .is greatly. reduced in a short time as previously described. The novelty of our invention is thata combination of etherification with epichlorohydrin and oxidation with periodate and chlorous acid produces anew starch modificationv whose function is completely; difierent than that of etherified starch, and a decided improvement over that of the non-cross-linked' dicarboxyl starches: The outstandingviscosity stability successively oxidized with many industrial uses of starch products. Uniformity of hot paste viscosity is required in starch derivatives used in the formulation of adhesives in order to maintain a coating of the adhesive film of uniform thickness on modern Stability of hot paste viscosity is also of importance in the high-speed coating of paper for the same reason. As another illustration we have the sizing and finishing of textiles in which the extent of penetration of the starch dispersion into the fiber is 0f commercial importance also is the fact that such hot viscous solutions after cooling and remaining at room temperature for several days can be reheated to efiect the originalhot paste viscosity. It is thus possible to utilize a hot dispersion of the product in a paper coating operation and to allow unused paste to cool during the weekend shut-down of the plant and then reheat the paste to essentially its original hot viscosity and texture for use when the plant begins its regular weekly schedule.

The improved properties described are of particular value in the use of starch in the food processing and pharmaceutical industries as a thickening, stabilizing, dis

persing, and suspending agent, and in paper and textile manufacturing as a sizing and coating material. Other applications are in oil drilling fluids, paints, printing inks and ceramics as a hydrocolloid additive." Still other industrial useswhere stability of viscosity of aqueous dispersions of starch and its derived products 'are of importance will be apparent to those familiar with the art.

Of commercial significance also is the fact that the consecutive reactions of'etherificationand oxidation to produce the cross-linked dicarboxyl Istarches can be conducted in aqueous suspension at room temperature which avoids the possibility of gelatinization of the starch granules during reaction. This allows ready filtration of the final product and its intermediate products and washing of these materials with water.

It is the prime objectofthe present invention to stabilize starch and starch derivatives by actual chemical change in the'starch structure. This chemical change is effected by crosslinking the starch by etherification with epichlorohydrin within the range of 200 to 2000 anhydroglucose units per cross-link followed by periodate and chlorous acid oxidation to the extent of from 0.5 to 5 percent dicarboxyl content. Although this range of oxidation is preferred, the invention is not limited to it. Cross-linked dicarboxyl starches from 5 to essentially percent dicarboxyl content can readily be prepared but at considerably higher cost and would appear to be of value only in special cases. The crosslinked dicarboxyl starches are isolated as their neutral sodium, potassium or ammonium salts or mixtures of these salts. They may also be isolated in the free acid forms. i

In order to calculate the amount of epichlorohydrin to be used the structural formula of the recurring anhydroglucose units in starch may be represented as CHIOH I -0 i mag L..-

Patented Mar. 22, 1960 3 b a c the figures) of the starch molecule with the reactive aqueous pastes of the product had mcreased viscosity groups of a molecule of epichlorohydrin. Since there are stability, water holding capacity and clarlty over those of 3 hydroxyl groups in an anhydroglucose unit of starch cooked pastes of the original starch and of noncrossand 2 reactive groups in epichlorohydrin, there would be linked one percent dicarboxyl starch.

required 1.5 moles of epichlorohydrin per mole of starch 6 v for complete cross-linking of all of the hydroxyl groups Example 2 in the anhydroglucose units of starch. A completely reacted Starch could then be represented as containing Two hundred ml. of a stock aqueous solution containcross-links per anhydroglucose unit or 0.67 anhydrogluing 1.33 gms. of sodium hydroxide and 33.4 gmg, of

cose units percross-link. l0 hydrous sodium sulfate was prepared. To 150 ml. of The products Of the invention are cross-linked to the this solution 100 gms. of cornstarch was added and y minor extent of 2000 t0 200 anhydroglucose units slurried by mechanical stirring. A solution of epichlorop cross-link which s 0-034 percent l p ent of hydrin in 50 ml. of the stock solution was next added e reaction of all of the xy ps n starch ith to the starch slurry and the mixture stirred at 25 C. for epichlorohydrin. Degree of cross-linking is determined 18 hours. The amount of epichlorohydrin was suflicient by analysis of the etherified starch filtrate for unreacted to produce cross-linking to the extent of 610 andhydroepichlorohydrin. The procedures for oxidation with glucose units per cross-link asdcterininedby analysis. periodate and chlorous acid are essentially the same as The mixture was neutralized with 6 N sulfuric acid from those described in the aforementioned -Patent No. pH 1 1.2;to-p;H 2.50. Without filtering a.solution-of 3.96 2,894,945. The granular state of starch is maintained 20 gms, ofpglium metaperiodate in 53 ml. of. Water was throughoutthe above reactions and the reaction products addedslowly and the mixture stirredrapidly during the are therefore composed of granules substantially in their addition. The reaction was carried out at room temperaoriginal unswollen form. ture and allowed to continue for one-half hour. The

The formula below represents a possible segment of resulting dialdehyde starch was filtered off and washed the structure of the cross-linked dicarboxyl starches for with water. The wet material was resuspended in 113 illustration only where A is a crosselinked anhydrogluml. water and 27 ml. of an aqueous solution containing cose unit of the modified starch, B is an anhydroglucose 13.33-gms. of sodium chlorite was added very slowly to unit of the modified starch, and C is a dicarboxyl unit as the stirred slurry. At the same time, 6 N'sulfuric acid the disodium salt of the modified starch. The formula, was slowly added to the reaction mixture. The relative however, is not limited to this segment as numerous other 30 rates of addition of the chlorite and sulfuric acid solucombinations of cross-linking and dicarboxylation are tions were such that a pH value of near 4 was maintained. obvious to those familiar with the art, for the fulfillment The total 6 N sulfuric acid required to bring the pH back of ,the specifications described earlier, and where It may to its original value of 3.23 was 7.8 ml. The method vary from 200 to 2000. of isolation was the same asin'Example 1. This product ether cross-link (EH 0 CHeOH CHaOH I i I J COONa (rooms.

I: OH H DE A B o The following examples will further illustrate the emhad a dicarbo'xyl content of 3 percent and its aqueous bodiment of the invention. hot pastes hadf'good viscosity stability and clarity.

Example 1 Example-3 Two hundred ml. of a stock aqueous'solution contain- One hundred grams of"starch"wa's'j treated as described ing 1.33 gms. of sodium hydroxide and 33.41 gms. of in Example 2'up to the con'clusionof the oxidation with anhydrous sodium sulfate was prepared. To 150 mlfof sodium metaperiodate. At this point instead of isolating this solution 100 grams of corn starch was added and the material the 2.7'ml. of a sodium 'chlorite solution slurried by mechanical stirring in a closed system. A containing 13.33 gms. was added directly to the dialdesolution of 0.0519 gram of eipchlorohydrin in 50 ml. of hyde starch slurry in the reaction mixture. The addition the stock solution Was next added to the starch slurry was made slowly with a simultaneous addition of 6 N and the mixtures-timed at 25 C. for 18 hours. The mixsulfuric acid with the relative rates of addition so adture was neutralized with sulfuric acid, filtered and washed iusted as to maintain the pH of the rea i mixture D with water. The degree of cross-linking was 1390 an- 4. The isolation of'this product is similar to that dehydroglucose units per cross-link by analysis. The wet scribed in Exampl The Product was the Same as the product was slurried in 450 ml. of water and 800ml. product describe i Example of water containing 1.32 grams of sodium periodate were i added in 30 minutes with continuousstirring of the 'mix- I Example}, rure. After 10 minutes the starch was filtered off and one hundred grams of'comstarch was cross'lmked as washed with water. The wet material was suspended in destilibefil n p e 2 t0 Yild 335 Y F E "Hits 113 ml. of water and 27 ml. of aqueous solution containas D o -l nkh reaction mixture was neutral ing 13.33 grams of sodiu hl i and 42 1 f glacial ized with 6 N sulfuricacid. Without filtering, a solution acetic acid added. After stirring at room temperature of of sodiumemstaperiodate 53 Water for 3 hours'the reaction Was complete and the mixture was. added slowly and the'miixtul'e stirred fapidlyduring was filtered and the product washed 3 times with water the addition. The reaction was carried out at room tem- While suspended in the third Wash a solution of 0.5 N Pel'atm'eand:allowed'to-cominue for one'half hour- The Sodium hydroxide Was added until h l r pH was 9 resulting dialdehyde starch 'was filtered off and washed inorder to neutralize all of the carboxyl groups. The airith Wa'ten- The wet-material was re-s p in 185 dried cross-linked product had a dicarboxyl content of ml. water (including indistu'm inthti filieled cake) and one percent, 1.6,, one anhydroglucose unit per in 44 ml. ore-an aqueous solutioncontaining 22.23 gms.'of

starch had been converted to a dicarboxyl unit. Cookcd rs sodiumvchiorite was added :very slowly to the stirred slurry. At the'same time, 6 N sulfuric acid was slowly added to the reaction mixture. The relative rates of addition of the chlorite and sulfuric acid solutions were such that a pH value of near 4 was maintained. The total 6 N sulfuric acid required was 17 ml. The product was isolated by filtration and washed two times with water. The third wash was done with 20 percent (by volume) methanol in Water and while suspended, the slurry pH was adjusted to pH 9.0. One additional wash in 20 percent methanol was given prior to isolation by filtration and air drying. This product had a dicarboxyl content of 5 percent and its hot paste viscosity was the highest of the various products whose preparations are described in the various examples. Viscosity stability of the hot paste was greater'than that of a comparable noncross-linked dicarboxyl starch.

We claim:

1. A modified starch in the form of ungelatinized granules having the properties of improved viscositystability and clarity in aqueous dispersion under normal gelatinizing conditions and of forming a reversible paste" upon' cooling, said modified starch being obtained by reacting one mole equivalent of unmodified starch granules with from 0.0005 to .005 mole equivalent of epichlorohydrin to etherify and intermolecularly cross-link one out of every 200-2000 anhydroglucose unitsand then treating the cross-linked starch successively with sodium periodate and chlorous acid to form a substantially dicarboxylated starch.

2. A modified starch according to claim 1 in which the extent of oxidation with sodium periodate is in the range 0.5 to 5 percent conversion of the anhydroglucose units in the etherified starch to dialdehyde units and in which essentially all of the dialdehyde units are subsequently oxidized with chlorous acid to dicarboxyl units.

3. Themodified starch of claim 2 in which theca'rboxyl groups of the dicarboxyl units are present in the free acid form. i

4. The modified starch of claim 2 in which the carboxyl groups of the dicarboxyl units are present as sodium salts.

5. The modified starch of claim 2 in which the carboxyl groups of the dicarboxyl units are present as'potassium salts.

6. The modified starch of claim 2 in which the carboxyl groups of the dicarboxyl units are present as ammonium salts.

References Cited in the file of this patent UNITED STATES PATENTS 2,548,455 Walker-ct al. Apr. 10, 1951 2,802,000 Caldwell et al. Aug. 6, 1957 2,853,484 Lolkema et a1. Sept. 23, 1958 2,894,945 Hofreiter et al. July 14, 1959 OTHER REFERENCES Radley: The Oxidation of Starch, Manufacturing Chemist and Manufacturing Perfume, July 1942, XIII, 7 pp. 158-166. 

1. A MODIFIED STARCH IN THE FORM OF UNGELATINIZED GRANULES HAVING THE PROPERTIES OF IMPROVED VISCOSITYSTABILITY AND CLARITY IN AQUEOUS DISPERSION UNDER NORMAL GELATINIZING CONDITIONS AND OF FORMING A REVERSIBLE PASTE UPON COOLING, SAID MODIFIED STARCH BEING OBTAINED BY REACTING ONE MOLE EQUIVALENT OF UNMODIFIED STARCH GRANULES WITH FROM 0.0005 TO .005 MOLE EQUIVALENT OF EPICHLOROHYDRIN TO ETHERIFY AND INTERMOLECULARLY CROSS-LINK ONE OUT OF EVERY 200-2000 ANHYDROGLUCOSE UNITS AND THEN TREATING THE CROSS-LINKED STARCH SUCCESSIVELY WITH SODIUM PERODIATE AND CHLOROUS ACID TO FORM A SUBSTANTIALLY DICARBOXYLATED STARCH. 